It's actually pretty easy. Buy a bit off eBay, watch a few YouTube video, practice on an old tank, or old glass of some sort, then mark and drill your own. That's what I did. The bit is pretty cheap and I've drilled a lot of holes with it. It's still good and I have been fortunate enough to not have any breaks. Just make sure to get the right size bit for your bulkhead. And keep a little water running while you drill. The last few cm are the toughes. I tend to spald a small piece off the inside of the cut each time but everything still seals well.

"Good things happen to those who wait" so I'm gonna continue to kick back, put my feet up and wait. Should I happen to get the urge to do otherwise I'll close my eyes and wait for the feeling to pass.